A typical image reading apparatus has a structure as shown in FIG. 1. In FIG. 1, the image reading apparatus has a body 11 and a cover 13. The body 11 houses many elements, including optical members, mechanical elements and electrical circuits. The cover 13 covers a document exposure base 12 (see FIG. 2) on the body 13. The document exposure base 12 is made of a light translucent material, e.g., glass. A document containing an image to be read is held between the document exposure base 12 and the cover 13. The body 11 is further provided with a control panel 14 on the front of the body 11 so that the control panel 14 is exposed.
The image reading apparatus has a scanner 15. The scanner 15 is provided below the document exposure base 12, as shown in FIG. 2. The scanner 15 moves along the document exposure base 12 and optically scans an image on a document D which is held between the document exposure base 12 and the cover 13. The scanner 15 has a light source 16, a focus lens 17, a photoelectric transducer 18 and a carriage 19. The light source 16 illuminates the ducument D. The focus lens 17 optically picks up the document images and focuses the images on the photoelectric transducer 18. The photoelectric transducer 18 generates electrical outputs in response to the document images.
The photoelectric transducer 18 has a photo detector, for instance, a CCD (Charge Coupled Device) line sensor for reading the document images in a line along the CCD line sensor. The CCD line sensor of the photoelectric transducer 18 has a resolution of, for instance, 16 lines/mm for its longitudinal direction, or the direction perpendicular to the scanning direction of the scanner 15.
The scanner 15 is driven by a scanner driving mechanism, as shown in FIG. 3. The scanner driving mechanism has a guide rail 21, a guide rod 22, a timing belt 25 and a pulse motor 26. The guide rail 21, the guide rod 22 and the timing belt 25 are disposed along the scanning direction. The carriage 19 is provided with a roller 20 at one end. The roller 20 has been designed to travel on the guide rail 21. Further, at another end of the carriage 19, the guide rod 22 passes through the carriage 19. Thus, the carriage 19 is movable along the guide rail 21 and the guide rod 22.
The carriage 19 is fixed to the timing belt 25. The timing belt 25 is suspended between two pulleys 23 and 24. One of the pulleys 23 and 24, e.g., the pulley 24, is coupled to the pulse motor 26. Thus, the scanner 15 is driven in the scanning direction by the pulse motor 26.
Generally, such an image reading apparatus, as described above, is provided with a read region designator which designates a region of document images to be read. The read region designator consists of an electrical circuit (not shown). When reading a specified region of the document image, coordinate dimensions of the specified region are determined by manual operation of a keyboard of any equipment coupled to the scanner 15. Therefore, it takes much time to designate a specified region to be read. Further, if many regions of the document are to be read, the designating process becomes very complicated.
Another method has been used in the past for designating an image reading region. According to the method, all images on a document are first read and displayed on a display screen of a device, such as an image processor. A specified region of the image to be read is then designated by using a pointing device, e.g., a mouse.
However, this type of image reading apparatus has a considerably high resolution, for instance, 4 lines/mm, 8 lines/mm or 16 lines/mm. If, for instance, the entire document image in an A3 size is read in three colors of R, G and B, 256 gradations and a resolution of 16 lines/mm, the conventional image reading apparatus needs an image memory with a large volume, i.e., more than 95 M bytes (mega bytes). Further, the conventional image reading apparatus described above is slow in designating regions of document images to be read.